A standard solar collector has an absorber surface on both the top and bottom faces with a flow passage for a heat-transfer medium between the absorber surfaces. A plurality of connecting pieces or nipples are provided on edges of the absorber unit. As a rule, several such solar collectors are connected together to form a solar-collector field. For this purpose the solar collectors are connected to one another via their connectors to form the solar collector fields, either in parallel or in series. For a connection in series, the heat-transfer medium flows through the interconnected solar collectors one after the other. The heat-transfer medium is normally water, which as a rule flows over the entire surfaces of the two panels forming the flat solar collectors.
In practice, the solar collectors described above are known in various embodiments. Each solar collector usually has two connectors, each being provided for the intake or output of the heat-transfer medium. The two connectors are positioned either on one side of the solar collector or at diagonally opposite corners of the solar collector. Limits are imposed on these solar collectors with regard to their interconnection to form collector fields. Only specific configurations or connections of solar collectors are possible, or long paths must disadvantageously be provided between the solar collectors. As a result, the effectiveness of the heat transfer in solar collector fields leaves much to be desired for the known solar collectors. In the known solar collectors, a vent is frequently provided in an output line to the solar collector. The operational reliability of the ventilation often leaves much to be desired.